Finally got rid of the exhaust problem with my 300TD Turbo Wagon
 

I have had the car for three years now and have been plagued with the problem of exhaust coming in through the rear hatch. I replaced the rubber weather seal on the hatch and took out shims from the latch to make it close tighter. This helped a bit, but I was still getting fumes if I opened the front windows. I have no AC, so in the summer I was always playing musical windows. I finally took it to a muffler shop recommended by a local Mercedes mechanic who they use. They took the tail pipe comming from the muffler and cut it off so it faces to the drivers side instead of straight back. Then they extended it so it is flush with the rear side body. All the exhaust is now blown straight to the side as I drive and doesn't get caught in the back draft behind the car were it was coming in. Many pickup trucks have the exhaust facing sideways because it ends up comming in the back window of the cab.
Why didn't I do this mod sooner?

Because your problem should have been solved by other means. I've had three wagons stock wagons and no exhaust issues. My sonic wagon is about to get mufflerless or a giant hole straight thru it however- strictly for power.

What other means are there besides duct tape?

Assuming your wagon is a W123 like mine, someone must have installed a sedan muffler on yours. Mine has the sedan muffler, which exists out the back vs. the wagon muffer, which exists out to the side.

mine comes out the back. sideways.

http://i42.photobucket.com/albums/e3...h/DSCN2117.jpg

Wagons have a little vacuum pocket following them when moving. It increases highway efficiency but it means exhaust will circle around in that pocket unless its routed out the side.

Pictures of the new tailpipe and the carbon from the leak
 

I don't think a link to an image on your desktop is going to help much here!:D

You had an improper muffler put on.

That link to my desktop was an artifact of my trying to post an image here for the first time. As to the muffler, it came with the car. I just had the tail pipe cut before where it use to turned 90 deg. to the back and extended a bit further.